Anodic polarization of stainless steel alloys in molten NaNO3KNO3 eutectic mixture

• Published in: Anti-corrosion methods and materials Vol. 48; no. 2; pp. 99 - 107
• Main Authors: AbdelHakim Ali, H.A., Attia, A.A., AlMasri, A.N., Baraka, A.M.
• Format: Journal Article
• Language: English
• Published: MCB UP Ltd 01-04-2001
• Subjects: Alloys; Corrosion resistance; Oxidation; Stainless steel
• ISSN: 0003-5599
• DOI: 10.1108/00035590110384083

This article presents the galvanostatic anodic oxidation of two types of stainless steel alloys, ferritic 15.03 Cr and austenitic 20.45 Cr, 8.37 Ni, in molten NaNO3KNO3 eutectic mixture at different temperatures ranging from 673873K. At a temperature of 673K the shape of polarization curves for the alloys is complex, while at higher temperatures it is simple. The passivity potential range was calculated as the difference between the passivation potential, Ep, and the breakdown potential, Eb. The value of Eb Ep decreases with the increase of temperature. The amount of iron, chromium and nickel dissolved in the melt was determined after each experiment using atomic absorption spectroscopy. The composition and structure of the corrosion products formed on the surface of electrodes were examined by Xray diffraction analysis. Corrosion parameters derived from the polarization curves are calculated these are polarization resistance at low current densities, Rp, exchange current density, io, corrosion current density, icorr, passivation current density, ip. It was found that the increase of temperature increases io, icorr, and ip while Rp, decreases. From these results it was found that, under the given conditions, the austenitic stainless steel alloy is more corrosion resistant than the ferritic one. The activation energy of corrosion was estimated for the two alloys.